This invention relates to high-density light emitting semiconductor device arrays and, more particularly, to a light emitting diode (LED) array having optical elements directed toward optimizing high-density packing of the LEDs in balance with collection and collimation of the LEDs' radiant output.
Light-emitting semiconductor devices may be arranged in various configurations, such as arrays, for lighting applications. Examples of these applications include: lithographic processes used, e.g., in fabricating semiconductor devices, and curing processes used, e.g., for ink printing and fabrication of DVDs. These applications generally have associated parameters, including, e.g., a photoreaction may contemplate provision of one or more radiant power densities at the work surface, at one or more wavelengths, applied over one or more periods of time and within thermal limitations.
In these applications, the light emitting semiconductor devices generally are employed to deliver against the parameters. At the same time, the light emitting semiconductor devices typically have certain operating characteristics and specifications. The characteristics include: total power emitted; power stability; radiance; radiant intensity; the wavelength(s) of the radiant output; the coherence of the radiant output; the collimation of the radiant output; as well as other operative functionalities provided by the semiconductor device as a light system (e.g., ability to provide pulsed operation and/or effective thermal management). In turn, the light emitting semiconductor device's specifications generally are associated with its fabrication and, among other things, are directed to preclude destruction and/or forestall degradation of the devices. These specifications generally include operating temperatures and applied, electrical power.
Where the application requires delivery of a relatively high radiant power density at or across the work surface, a LED array may have some difficulty in that delivery. That follows because a typical LED in an array has a widely distributed radiant output. Indeed, a typical LED mounted alone on a planar substrate will exhibit a radiant output distributed characteristically across the hemisphere centered at the LED. Given such distribution, only some portion, often relatively small, of that radiant output is directed toward the work surface, thus diminishing the radiant power density at or across the surface. Moreover, such distribution implicates that, as the work surface becomes more physically separated from the LED, the radiant power density at or across the work surface will decrease rapidly, i.e., the decrease generally is anticipated to be proportional to the square of the separation.
Several approaches may be used to achieve radiant power density from a LED array so as to properly perform a particular process. In one example approach, a basic LED array may simply be disposed physically proximate the work surface. However, even if close proximity delivers appropriate power density, this approach generally is undesirable because, e.g., close proximity tends to necessitate undesirable changes to tooling and/or shielding. In another example approach, an array may locate conventional refractive lenses above the LEDs. This approach contemplates that each LED is associated with a conventional lens so that the lens collects and collimates the LED's radiant output. While this approach will tend to increase radiant power density, collecting and collimated a substantial preponderance of any LED's distributed radiant output contemplates a lens having a relatively large diameter, as well as other challenges. While this provides some performance increase, achieving the necessary diameter may be difficult, if not impossible. Moreover, using a lens of such diameter may be at odds with use of a densely-packed LED array and, as such, would be undesirable.
Another example approach to enhancing radiant power density contemplates using conventional reflective optics. In this approach, a LED is mounted in a reflector (e.g., having a parabolic form). Unlike refractive optics, reflective optics generally collect and collimate a substantial portion of the LED's radiant output. Even so, conventional reflective optics generally are not used in a tightly packed or dense array because of their size. For example, a typical application of conventional reflective optics is illustrated by LED flashlights in which one or more LEDs are mounted in a large reflective optic, so that the optic collects light from such LEDs.
Accordingly, there is a need for high-density light emitting semiconductor device array and, more particularly, for LED arrays having optical elements directed toward optimizing high-density packing of the LEDs in balance with collection and collimation of the LEDs' radiant output.